The present invention relates to a permanent magnet rotary motor in which a rotor including rotor magnetic pole sections formed of permanent magnets rotates.
Permanent magnet rotary motors have the rotor and a stator. Some rotors have a rotor core and the rotor magnetic pole sections formed of the permanent magnets. Some stators have a stator core including a plurality of stator magnetic pole sections, a plurality of slots having openings that open toward the rotor core, and exciting windings of at least two phases wound on these stator magnetic pole sections. It is known that, in the motor that uses the permanent magnets for the rotor magnetic pole sections, pulsating torque (cogging torque) and a thrust force are produced at the time of no-load operation. Such cogging torque hinders smooth rotation of the motor, thus causing vibration and speed variation of the motor. As an approach to reducing the cogging torque, there have been hitherto proposed formation of a slot with an oblique groove, hereinafter referred to as a skew, in the stator core or the rotor core, or use of a permanent magnet with the center of an inner circular arc thereof not aligned with the center of an outer circular arc thereof, hereinafter referred to as the permanent magnet of an eccentric type. However, formation of the skew may reduce the torque or reduce the productivity of the motor. Further, use of the permanent magnet of the eccentric type cannot increase the magnetic flux density of the motor, so that higher torque density cannot be achieved.
Then, in order to address these problems, Japanese Patent Application Laid-Open Publication No. 15967/2004 (Patent Document 1) discloses a permanent magnet rotary motor in which each of stator magnetic pole sections of a first type and each of stator magnetic pole sections of a second type are arranged alternately. Each of the stator magnetic pole sections of the first type has a pair of projecting portions that project in the peripheral directions of a rotor in a magnetic pole surface portion provided at the leading end of the stator magnetic pole section. On the other hand, each of the stator magnetic pole sections of the second type does not have the pair of projecting portions. In this permanent magnet rotary motor, at the tip of each stator magnetic pole section, a torque pattern having a waveform different from that of a torque pattern generated at the tip of other stator magnetic pole section adjacent thereto is generated. A variation in the torque generated in adjacent stator magnetic pole sections are thereby cancelled out with each other, thus preventing the cogging torque generated in the rotor.
In the permanent magnet rotary motor disclosed in Japanese Patent No. 3505347 (Patent Document 2), each of the two types of stator magnetic pole sections are alternately arranged in the peripheral direction of a rotor. The dimensions of the magnetic pole surfaces of the two types of stator magnetic pole sections in the peripheral direction are different.
Further, in a permanent magnet rotary motor disclosed in Japanese Patent Application Laid-Open Publication No. 178298/1999 (Patent Document 3), each of the two types of stator magnetic pole sections is alternately arranged in the peripheral direction of a rotor. The curvatures of the magnetic pole surfaces of the two types of the stator magnetic pole sections are different.
In a permanent magnet rotary motor disclosed in Japanese Patent Application Laid-Open Publication No. 309625/2001 (Patent Document 4), widths of openings of a plurality of slots formed in a stator core in the peripheral direction of a rotor are made different alternately.
In the permanent magnet rotary motor constituting the stator core as described above, however, two types of divided cores having different shapes of the projecting portions provided at the leading ends of the stator magnetic pole sections must be prepared. Thus, in order to manufacture the stator core, the number of component types must be increased, and manufacture of the assembly of the stator core thus may become complicated.
In the permanent magnet rotary motor in Patent Document 4, in particular, has eight poles and 24 slots. Accordingly, a least common multiple LCM (P, N) of the number of rotor magnetic pole sections P(8) and the number of slots N (24) and a least multiple LCM (P/2, N) of a half of the number of the rotor magnetic pole sections ½ P(8) and the number of the slots N(24) are an equal value of 24. Further, phase of a current flowing through two of adjacent windings arranged in the peripheral direction of the rotor are shifted as indicated in the sequence of +U, +U, +V, +V, +W, +W, and the like so that currents that flow through the adjacent windings have a phase difference of an electrical angle of 120° respectively. When the open angles of the slots are set as described above in such the permanent magnet rotary motor, magnetic leakage flux is suppressed. An induced voltage is therefore improved. However, the torque is reduced, so that torque ripple is increased.